1. Field of the Invention
This invention relates to the field of edge bending metal stock. More particularly, this invention relates to the field of dies used in bending machines, and a method of simultaneously bending a piece of handrail cap stock and a piece of handrail channel stock.
2. Description of the Prior Art
In the installation of stair railings, several components are utilized: a length of channel stock is located 3 or 4 inches above the floor, a length of molded handrail cap stock is located approximately 3 feet above the floor, and plurality of spokes are mounted vertically between the handrail and the bottom channel approximately 4 or 5 inches apart from each other. Both the handrail and the bottom channel are parallel with the floor or stairway incline, and must be bent in a return bend to follow a winding stairway down or up.
Formerly, the lengths of cap stock and channel stock had to be bent in separate operations in a bending machine utilizing a radius block and in which the stock had to be continuously fed through the apparatus to achieve the desired curvature. The problems experience with "feed through" type production bending are that the bending process is slow, and that, since the amount of feed is regulated by the operator, the degree and trueness of the arc of curvature varies from piece to piece and operator to operator. These problems are magnified in the situation where two pieces, the channel piece and the handrail cap piece, must be mated in the final stair railing.
Methods and apparatus for "single pull" edge bending of flat stock without distortion or structural damage to the stock have been developed. Such systems utilize a stationary die to block movement of one end of the stock, called a back block, a die with a circular arc of predetermined radius around which the stock is to be bent, called a forming die, and a die to engage the stock along its unblocked portion and bend it around the forming die, called a drawing block. The drawing block is generally supported in an assembly which swings around the forming die by a roller block which rolls along the back surface of the drawing block. Once the stock has been placed between the forming die and drawing block, with one end blocked by the back block, the drawing block can be swung around the forming die in a single pull to achieve a bend of anywhere between 0.degree. and approximately 180.degree.. Such apparatus can be adapted to bend single pieces of stock having a fairly uniform cross section across their width, such as flat stock, or handrail cap stock, with no distortion. But twisting or distortion cannot be avoided if a piece of stock not having a generally uniform cross section across its width, such as the channel stock with its web and two flanges, is bent in such a bending operation. Thus, in order to shape the pieces of stock used to assemble a stair railing utilizing the previously known methods, the handrail cap stock can be bent in a single pull operation, but the bottom channel has to be bent in a separate operation. The problem of non-matching mate pieces remained unsolved until the present invention.